**Core Concept**
Ketamine is a non-barbiturate anesthetic agent that induces dissociative anesthesia through its action on the central nervous system. It is often used in emergency medicine, anesthesia, and pain management. The disadvantage of ketamine is related to its mechanism of action and side effect profile.

**Why the Correct Answer is Right**
Ketamine acts as an N-methyl-D-aspartate (NMDA) receptor antagonist, which can lead to hallucinations, delirium, and other psychotomimetic effects. Additionally, ketamine can cause increases in intracranial pressure (ICP) and can be problematic in patients with head injuries or increased ICP. This makes ketamine a less desirable choice in certain clinical scenarios.

**Why Each Wrong Option is Incorrect**
**Option A:** While ketamine can cause increased heart rate and blood pressure, this is not the primary disadvantage associated with its use.
**Option B:** Ketamine is known for its analgesic and anesthetic properties, making it a valuable medication in the right context.
**Option C:** Although ketamine can cause nausea and vomiting, this is a common side effect of many anesthetic agents and not the primary disadvantage of ketamine.

**Clinical Pearl / High-Yield Fact**
When using ketamine, it's essential to monitor patients for signs of increased ICP and to be aware of the potential for psychotomimetic effects, especially in patients with a history of psychiatric disorders.

**Correct Answer: D. Increased intracranial pressure and psychotomimetic effects.**